Laminated glass is most commonly found in automotive windshields and architectural building glass. Two outer sheets of glass are vulcanized to an interlayer, usually composed of polyvinyl butyral. Polyvinyl butyral is commonly used as an interlayer for safety glass and is used in sheet form, heat-laminated between glass sheets under pressure. However, polyvinyl butyral (PVB) compounds are very sensitive to warm temperatures, humidity, and most solvents prior to lamination, so that using them with any combination of paint or ink directly applied is almost impossible.
There has been very little use of decorative interlayer materials in order to create architectural glass graphics for applications, such as windows and signage. Printing directly onto the glass and then laminating with PVB is a method currently used, however, it is cumbersome and ineffective because the interlayer is laminating to the ink film and not bonding directly to the glass in areas where the paint or ink covers the PVB interlayer. This method, therefore, works only when small areas of glass are used for a graphic display. Another method used to create glass graphics is the vinyl-stencil method. Cut-out vinyls are first adhered to the glass and then laminated with PVB. There is some success with this process, however, it is very costly and time-consuming and there is a very high failure rate with large surface areas covered by the graphic. Also, most polyvinyl stenciling materials are not light-fast.
It is known to replace the polyvinyl butyral interlayer with a composition of polyurethane as taught in U.S. Pat. No. 3,509,015. In this instance, the polyurethane interlayer is cast in place from a pourable resin. Decorative effects may be obtained by coloring the resin prior to lamination.
U.S. Pat. No. 3,640,798 discloses a method of applying a colored self-vulcanizing paste onto a cellular foam plastic interlayer, which is then mechanically sandwiched between two pieces of glass. The paste must be hand applied with a knife, or be applied by stamping or molding processes, applied directly to the cellular foam plastic interlayer. This construction limits the mass production possibilities.
As outlined above, the various processes which have been used to create a graphic or color image sealed between layers of glass require heavy or large machinery and, in some cases, very expensive die-cutting materials. Most of the processes must be maintained in temperature and humidity-controlled environments which are required for handling the polyvinyl butyral materials. In addition, only small areas where the graphic covers the glass are possible, the coloring materials are not light-fast and a very high failure rate usually occurs. Where the materials are not molecularly fused (heat-laminated), the composite is often not permanent.
No one before has been able to achieve mass production printing on a transparent interlayer fused by heat lamination between sheets of glass to yield a unitary, permanent, graphic panel.